Method of producing cis-1,4-polyisoprene

ABSTRACT

Isoprene is readily polymerized to have over 90 percent repeating isoprene units in the 1,4-cis configuration if the polymerization catalyst employed is prepared by reaction of titanium tetrachloride with an excess of dialkylaluminum fluoride. The proportions of the reactants are not critical because the resulting reduction of TiIV does not go beyond TiIII. The alkyl bound to aluminum should have 1 to 5 carbon atoms. Ethers may be added to the catalyst reaction mixture.

United States Patent Inventors Appl. No.

Priority Helena Antropiusova Prague;

Karel Mach, Roztoky u Prahy; Bohumir Matsyska, Horni Pocernice; Jaromif Trneny, Kralupy nad VL ta vou; Cestmir Vyroubal, Kralupy nad VL ta vou, all of Czechoslovakia Oct. 28, 1968 Sept. 21, 1971 Ceskoslovenska akademie ved Prague, Czechoslovakia May 18, 1967 Czechoslovakia Continuation-impart of application Ser. No.

729,896, May 17, 1968, now abandoned.

METHOD OF PRODUCING ClS-1,4- POLYISOPRENE 10 Claims, No Drawings [52] U.S. CI d 260/943 [51] lnt.Cl C08d 3/12 [50] Field of Search 260/943, 94.9 B

[56] References Cited UNITED STATES PATENTS 3,165,503 H1965 Kahn etal 260/943 3,065,220 5/1956 McManimie et al 260/949 3,224,980 12/1965 Swift 252/429 Primary Examiner--Joseph L. Schofer Assistant Examiner-Richard A. Gaither Attorney-Richard Low ABSTRACT: lsoprene is readily polymerized to have over 90 percent repeating isoprene units in the 1,4-cis configuration if METHOD OF PRODUCING CIS-l,4-POLYISOPRENE REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of our copending application Ser. No. 729,896, filed, May 17, 1968, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to the polymerization of isoprene, and particularly to the production of a polymer whose repeating units derived from isoprene, hereinafter referred to as isoprene units, are predominantly in the 1,4-cis configuration characteristic of natural rubber.

Polyisoprene approaches the desirable mechanical properties of natural rubber as the percentage of 1,4-cis-isoprene units approaches 100 percent. Polyisoprene containing more than 90 percent 1,4-cisisoprene units has been prepared heretofore by the polymerization of isoprene in the presence of Ziegler-Natta catalysts based on reaction products of alkylaluminum compounds and titanium halides prepared with or without small amounts of ethers, amines, or aminoethers which tend to hasten the polymerization, to increase the molecular weight of the polymer, and to reduce its gel content (see British Patent Nos. 856,317; 870,010; and 877,661 and French Patent No. 1,334,097, for example).

The methods for preparing the known catalysts are relatively inconvenient. The starting materials employed are trialkylaluminum and titanium tetrachloride, and must be mixed in carefully controlled amounts if useful results are to be achieved during the polymerization of isoprene, and it is particularly important that deviations from a mole ratio of 1:1 be limited to :20 percent with the generally preferred triisobutylaluminum. Diethylaluminum chloride has also been used as a catalyst ingredient, but must be combined with titanium trichloride prepared by a separate reduction of the tetrachloride. The bromides make very poor catalysts with titanium halides, and the dialkylaluminum iodides lack catalytic activity in combination with titanium halides.

SUMMARY OF THE INVENTION It has now been found that dialkylaluminum fluorides whose alkyl groups have one to five carbon atoms combine with titanium tetrachloride to form catalysts which re stereospecific in the polymerization of isoprene to predominantly 1,4-cis-polyisoprene while being capable of being prepared and used in a simple manner. The dialkylaluminum fluorides are prepared in a known manner and may be combined with titanium tetrachloride over a wide range of ratios, from 2:1 to 50:1, by merely keeping a mixture of the ingredients in a common inert, organic solvent at room temperature or below, preferably between 5 and 25 C., temperatures as low as l and as high as 30 C. being effective.

The reaction product is largely insoluble in organic solvents, and the entire heterogeneous reaction mixture including excess reagents may be contacted with isoprene to polymerize the latter under the usual polymerization conditions and at temperatures in the same range as those used in the catalyst formation. It will be appreciated that water and oxygen are to be excluded throughout the steps described above, the concentration of water and oxygen in the several reaction systems being held at maxima of about 20 and 15 ppm. respectively, as is conventional.

Best results have been obtained with the use of diethylaluminum fluoride, and the polymerization rate and polymer yield decrease with increasing length of the alkyl chain in the dialkylaluminum fluoride. The reaction becomes too slow and the yield too low for practical use with dioctylaluminum fluoride, and only the dipentylaluminum and lower alkylaluminum fluorides produce results which are economically acceptable.

The polymerization of isoprene in the method of the invention is performed in a solvent for isoprene, and the initial concentration of isoprene monomer in the polymerization mix ture consisting essentially of the catalyst described above, the isoprene, and the solvent should be between 3 percent and 30 percent by weight, if the reaction is performed in a batch process.

Small amounts of diaryl or alkylaryl ethers may be added to the dialkylaluminum fluoride prior to its reaction with the titanium tetrachloride in the preparation of the catalyst, the ethers referred to in the above mentioned patents being useful, and diphenyl ether and anisole being representative of the same. The mole ratio of the ether to the aluminum or the dialkylaluminum fluoride in the catalyst reaction mixture should be between 0.1:l and 1.5:1.

The polymerization conditions are not in themselves af- 'fected by the use of the catalyst of the invention instead of the known Ziegler-Natta catalysts, and the ratio of reactants used in preparing the catalyst has little effect on the outcome of the polymerization step as long as the broad limits outlined above are maintained. The polymerization equipment may be of the usual type and should provide for a protective atmosphere, nitrogen, argon, helium, and hydrocarbon vapors being common in this art. Agitation, is desirable as in any heterogeneous reaction system.

The novel features of this invention thus reside primarily in the catalyst mixture and in its preparation. The catalyst reaction mixture is prepared from a solution of the dialkylaluminum fluoride in an inert, liquid, organic solvent and from titanium tetrachloride either in the pure form or in organic solvent solution, hydrocarbons being the preferred solvents.

The mixture so prepared is permitted to age at a temperature indicated above. A reaction occurs within a period of 10 minutes to 5 hours, and usually within 1 to 2 hours. The protective atmosphere used in the preparation of the catalyst may consist of or include gaseous isoprene, and catalyst formation is not impeded by the presence of isoprene. Other compounds capable of reacting with the catalyst must be excluded or practically excluded as is well understood by those familiar with Fischer-Natta catalysts, the known catalyst inhibitors including carbon monoxide, carbon dioxide, acetylene, cyclopentadiene, and the like. If the catalyst is prepared in the presence of 1 to 5 moles isoprene per mole of dialkylaluminum fluoride, the induction period in the subsequent polymerization of isoprene is shortened.

The isoprene polymerization by means of the stereospeciflc catalysts of the invention is conveniently performed in a continuous operation at approximately constant isoprene monomer concentration in the polymerization mixture because of the noncriticality of the AlzTiratio in the preparation of the catalyst over the entire range from 2:1 to 50:1, and the availability of the entire catalyst reaction mixture for use in the subsequent polymerization. When a catalyst prepared by the method of the invention is used in batch polymerization of isoprene at decreasing monomer concentration, the mole ratio of aluminum to titanium is preferably held between 3:l and 15:1.

The solvent employed in the polymerization may be selected from a wide range of organic liquids inert to the reactants and the catalyst, including the commercially available liquid aliphatic, cycloaliphatic, and aromatic hydrocarbons and their industrial mixtures such as gasoline or diesel fuel, but also inert chlorinated hydrocarbons such as chlorobenezene.

The catalyst concentration in the polymerization mixture is not critical. It may vary, for example, between 0.5 and 20 millimoles titanium tetrachloride equivalent or titanium per liter of polymerization mixture. The pressure in the polymerization vessel is without significant influence on the result obtained, and may be higher or lower than atmospheric pressure to suit available equipment.

The isoprene monomer may be added to the polymerization mixture as a gas or as a liquid, either all at once or over the course of the polymerization reaction at a rate to keep its concentration constant. In the latter case, the monomer concentration in the polymerization is even less critical than in batch polymerization in which the initial isoprene concentration methanol acidified with hydrogen chloride. should be between 3 and 30 percent of the polymerization The polymer formed was recovered by filtration and washed mixtu by ig on the filter first with methanol containing phenyl-B- T p lym i n is terminated in a kn wn nn r h n naphtylamine as an antioxidant, and finally with water. When the desired conversion rate is achieved, and the catalyst is 5 1 d ied i a vacuum at 30 C., it weighed l.4 g. Its content of then deactivated and separated from the polymer formed. 1,4-cis-isomer was 93 percent, and its intrinsic viscosity was Methanol acidified with hydrogen chloride pure another al- 4.1 dl/g in benzene at 20 C. cohol may be added for this purpose together with a stabilizer, Example 2 r such as phenyl-B-n'aphthflamihe, The l mer b ined i The vessel of Example 1 was evacuated and charged with 30 washed free of residual catalyst and catalyst components by ml. benzene and 0.25 millimole titanium tetrachloride as in means of suitable solvents, such as alcohols and ultimately Example 1, and th reafter with 2 millimoles diisobutylaluwater, and dried. it may the b processed f th b th d minum fluoride dissolved in a small amount of benzene. The conventional in the handling of natural rubber because of its mixture Obtained by in u S irring was permitted to react content of 1,4-cis-polyisoprene which exceeds 90 percent. 1 2 hours 3 C The polymerization rate is increased and the gel content of lsopfene was introduced as in Example and the the polymer is decreased under otherwise identical conditions Q Polymerization Procedure descl'ibed 350? was followed- The if a small amount of one of the aforementioned others is added P y formed Weighed 8- contained Percem t the di lk l l i fl id d i preparation f the 1,4 units, and had an intrinsic viscosity of 3.4 dl/g in toluene at catalyst and prior to combining the dialkylaluminum fluoride 20 p 3 with the titanium tetrachloride. The amines and aminoethers A Pressure Vessel was carefully dried and purged y P 8 employed heretofore in this art are similarly effective, but best oxygen'h'ee nitrogen, and a Protective nitrogen results have been obtained with diphenyl ether and anisole. mosphel'e was maintained in the vessel throughout the The polyisoprene prepared by the method of th invention sequent steps. The vessel was charged with 90 ml. of a molar cannot be distinguished structurally from natural rubber by insolution of isoprene in nhexane- A catalysl was pared in frared analysis. Its molecular weight is high, and the intrinsic another vessel, similarly purged and fined with nitrogen from viscosity values obtained in toluene at C. are between 3.5 (178 of a Solution consisting of titanium d 7 d i i per gram (CH/g) tetrachloride per liter of n-hexane, and 8.8 ml. of a solution Th advantages f the dialkylaluminum fl id in the consisting of 22.17 g. diethylaluminum fluoride per liter of npreparation of catalysts in the method of the invention are be- 30 hexane- The Ticl and (QHsh were permitted to react lieved to be due in part to the fact that titanium tetrachloride for one and the Suspension hel'eafler obtained was is reduced by the dialkylaluminum fluorides of the invention trahsferred under a nitrogen blank F the Vessel containing to titanium trichloride at a practical rate, but not further. thelsoprehe soh'moh by h h ofalsyrmge- While the nature of the catalyst has not been fully elucidated The catalyzed Polymemahoh mixture was'smred at this time, it appears to consist essentially of a complex comfor 1 h whereupon the polymenzahhh was Stopped pound including aluminum absorbed to the surface of the by 'hlechhg 5 mh methanol cohtammg P 'B' titanium trichlorida naphthylamine into the liquid polymerization medium. The Any excess of dialkylaluminium fluoride present after for- Polymerization vessl was opehefji the pnolymer was mation of the catalyst is without influence on the activity of 40 recoverehwashed wlth methanol and at the camyst and on the amount and Properties of the The yield of polymer was 72.2 percent based on the polyisoprene formed. The preparation of the catalyst and its P h f it chmained percent use are thereby simplified in a manner not available heretoumts and had mmnslc vlscoslty Of3B dug m toluene at 30 fore.

The general procedure outlined above was also followed in DESCRIPTION OF PREFERRED EMBODIMENTS OF THE 45 the following series of polymerization runs 4 to 8 in which the 1 Th f n V-INVENTION amount of titanium tetrachloride used in preparing the e o owlhg exhmples h further hlustrahve of the catalyst and the amount of isoprene were kept constant. The method of the inventlon, and it should be underStOOd that the mole ratio of aluminum to titanium and the polymerization invention 15 not limited to the specific examples chosen for the time were varied as indicated in the following Table Diphenyl 2332 322 dlsclosure only ether was added to the diethylaluminum fluoride during preparation of the catalyst mixture in Runs Nos. 6 and 7 in the A glass pressure vessel g whh a mhghenc sun-er was listed mole ratio to titanium. The catalyst components were 22:11:35 2:3 :33? u g ge zz n e igh ist fgd tgg pennitted to react for one hour except in Run No. 5 in which p p u the catalyst components were permitted to react for 3 hours in into the evacuated vessel, followed by 0.25 millimole titanium the presence of2 8 moies isoprene per mole TL tetrachloride, and 1.75 millimole diethylaluminum fluoride in The table also lists the intrinsic viscosity 3 and the Solubility 1 ml. n-heptane. The mixture obtained by continuously stirof the polymer in toluene at C. is content of 1 units ring the contents of the vessel was held at 20 C. for one hour in percent, and the yield in percent f isoprene orig-many to form a catalyst by a chemical reaction resulting in the for- 60 present mation of a precipitate.

TABLE Mole ratio, cat'st Polym'n Soly, l,4'cls, Yield, Al/Tl Ether/Tl time, hours Dl./g. g./ l. percent percent 4 4. 54 b7 96. 2 so. a 3 5. l 69 96. 3 45 2 4.9 66 96. 0 62. 4 1 4. 61 97 95. 6 86. 6 2. 5 4. 52 62 94. 2 90. a

Enough gaseous isoprene was the n inthdduced ihtdthhg "W'ciaim. u a se] and dissolved in the liquid medium present to make the l. A method of producing polyisoprene having contents of concentration of monomeric isoprene in the mixture 3 percent 1,4 cis addition at least a high as 90 percent, consisting essenby weight. The isoprene consumed by polymerization was i y Ofthe Steps of! made up by introducing additional monomer into the vessel. a. holding a mixture of a dialkyialuminum fluoride and of After three hours, the monomer still present was drawn ofi titanium tetrachloride at a temperature between l0 and by evacuating the pressure vessel, whereby the polymerization 30 un il a po tio of a titanium tetfaChlOfide is was stopped. The catalyst was deactivated by adding 30 ml. reduced to titanium trichloride and a portion of the alu- 2. A method as set forth in claim 1, wherein at least one of said temperatures is between 5 and C.

3. A method as set forth in claim 1, wherein said temperatures are between 5 and 25 C.

4. A method as set forth in claim 1, wherein said mixture is held at said temperature in the presence of an aryl ether or an alkyl aryl ether, said ether being added to said dialkylaluminum fluoride in the preparation of said mixture prior to the mixing of the titanium tetrachloride with said dialkylaluminum fluoride, the mole ratio of said ether to said dialkylalu- 2O minum fluoride being between 0. 1 :1 and 1.5: l.

5. A method as set forth in claim 4, wherein said ether is diphenyl ether or anisole.

6. A method as set forth in claim 1, wherein said alkyl is ethyl.

7. A method as set forth in claim 1, wherein the initial amount of said isoprene held under polymeriztion conditions is between 3 and 30 percent of the combined weight of said catalyst, said solvent medium, and of said isoprene.

8. A method as set forth in claim 1, wherein said dialkylaluminum fluoride and said titanium tetrachloride are dissolved in a common, inert, liquid, organic solvent while said mixture thereof is held at said temperature.

9. A method as set forth in claim 8, wherein said solvent jointly with said catalyst and unreacted dialkylaluminum fluoride is contacted with said isoprene while holding said isoprene under said polymerization conditions.

10. A method as set forth in claim 8, wherein said organic solvent and said solvent medium are free from significant amounts of oxygen and moisture. 

2. A method as set forth in claim 1, wherein at least one of said temperatures is between 5 and 25* C.
 3. A method as set forth in claim 1, wherein said temperatures are between 5 and 25* C.
 4. A method as set forth in claim 1, wherein said mixture is held at said temperature in the presence of an aryl ether or an alkyl aryl ether, said ether being added to said dialkylaluminum fluoride in the preparation of said mixture prior to the mixing of the titanium tetrachloride with said dialkylaluminum fluoride, the mole ratio of said ether to said dialkylaluminum fluoride being between 0.1:1 and 1.5:1.
 5. A method as set forth in claim 4, wherein said ether is diphenyl ether or anisole.
 6. A method as set forth in claim 1, wherein said alkyl is ethyl.
 7. A method as set forth in claim 1, wherein the initial amount of said isoprene held under polymeriztion conditions is between 3 and 30 percent of the combined weight of said catalyst, said solvent medium, and of said isoprene.
 8. A method as set forth in claim 1, wherein said dialkylaluminum fluoride and said titanium tetrachloride are dissolved in a common, inert, liquid, organic solvent while said mixture thereof is held at said temperature.
 9. A method as set forth in claim 8, wherein said solvent jointly with said catalyst and unreacted dialkylaluminum fluoride is contacted with said isoprene while holding said isoprene under said polymerization conditions.
 10. A method as set forth in claim 8, wherein said organic solvent and said solvent medium are free from significant amounts of oxygen and moisture. 